Defoliant methods using thio esters of chloromethyl phosphonous and chloromethyl phosphonic acids



nited States atenit m Patented June 18, 1963 This invention relates to a new class of phosphonlate esters and a process for utilizing the same.

In particular, this invention relates to new chloromethylphosphonate compounds which have been found to have valuable properties as plant defoliants. These valuable properties are thought to be the result of a novel combiuation of the chloromethyl radical with various thio ester radicals.

The new compounds of this invention are the thio esters of chloromethylphosphonic acid, chloromethylphos phonous acid or chloromethylphosphonothiolic acid. They may be represented by the formula H oiommsn wherein R may be the same or different alkyl or aryl radicals, X may be oxygen or sulfur and n is or 1.

These compounds may be made by reacting a chloromethylphosphorus chloride with the desired thio alcohol, thio phenol, or their alkali metal salts. This is preferably done in the presence of an HCl acceptor such as sodium hydroxide, tertiary amines and the like, but will also proceed in the absence of such an acceptor. This reaction is illustrated as follows:

wherein R, X and n are defined as above and R' N is a tertiary amine, but may be another HCl acceptor as noted above.

which analyzed 14.8% P. Theory is P, 14.29 and had an index of refraction N =1.5559.

EXAMPLE 2.S,S-DI-TERT. BUTYL CHLOROMETHYLPHOSPHONODITHIOATE 'Following the procedure of Example 1, 51.0 grams of ClCH P(O) [SC(CH was prepared by reacting 41.8 grams of ClCH POCl in 10 ml. of benzene with 50 grams of (CH CSH and 55.2 grams of (C H N in 200 m1. of benzene. The resulting product analyzed 11.6% P compared to the theoretical value of 11.3% P. It had an index of refraction N =1.5317.

EXAMPLE 3 .S,S-DI-N-BUTYL CHLOROMETHYLPHOSPHONODITHIOATE To 50 grams of n-C H SH and 55 .2 grams of (C H N in 200 ml. oi benzene was added 42.1 grams of CICH POCI at 25-30 C. over a period of 16 minutes. The resultant mixture was allowed to stand for 16 hours at room temperature and then filtered. The filter cake was rinsed with 100 ml. of benzene and the benzene solution was then evaporated to give 61.3 grams of ClCH P(O) (SC H which had an index of refraction N =1.5287 and analyzed as 11.4% P and 24.8% S compared to the theoretical values of 11.3 P and 23.3 S. It boiled at 150-151 C. at 1 mm. Hg pressure.

EXAMPLE 4.S,S-DI-N-BUTYL CHLOROMETHYLPHOSPHONOTRITHIOATE Following the procedure of Example 3, except that 45.7

grams of ClCH P(S) C1 was used, 54.0 grams of ClCH P(S)(SC I-I was produced. This product had an index of refraction N =1.5661. It boiled at 163- -165 C. at 1.5 mm. Hg pressure, and analyzed 10.8% P

. and 33.1% S. The theoretical values are P, 10.6%; S,

Among the radicals which we have found suitable to N form the ester groups represented by R in the above formulas, are the methyl, ethyl, propyl, isopropyl, butyl, n-butyl, .amyl, octyl, decyl, phenyl, chlorophenyl, nitrophenyl and the like. In particular, we prefer the n-butyl radical because of the excellent defoliating properties of its esters.

It is surprising that these compounds should be such eflective defoliants since various other similar phosphonic acid thio esters have not demonstrated this property. Likewise, similar well-known chloromethylphosphonate esters do not have this property. As noted previously, it is thought to be the unique combination of the chloromethyl group and the thio ester group which provides the excellent defoliating action.

The following examples illustrate the products of this invention.

EXAMPLE 1.-S,S-DIETHYL CHLOROMETHYLPHOSPHONODITHIOATE To a solution of 35.0 grams of C H SH and 55.2 grams of (C H N in 200 of benzene is added 41.8 grams of ClCHgPOCl in 10 ml. of benzene. The mixture is stirred during the addition and the temperature is held at 25 30 C. The mixture contained considerable triethylamine hydrochloride and was then stirred at 25 30 C. for an additional 2 hours and then warmed to 50 C. for 2 hours. After cooling the amine hydrochloride was removed by filtration and the benzene distilled. The product boiled at 130 C. at 1 mm. of Hg pressure. 49.0 grams of ClCI-I P(O) (SC H resulted EXAMPLE 5.-S,S-DI-N-BUTYL CHLOROMETHYLPHOSPHONODITHIOI'I'E To 50.0 grams of n-C.,H SH and 55.2 grams of (C H N in 200 ml. of benzene were added 378 grams of ClCl-I PCl at 25 -30 C. over a 30 minute period. After standing 20 hours it was filtered and the cake washed with 100 ml. of benzene. After evaporation of the benzene, 44.0 grams of C1CH P(SC H resulted which had an index of refraction N =L5400 and boiled at 128-130 C. at 1 It analyzed as 11.8% P and 25.6% S compared to 12.0% P and 24.8% S theoretical.

EXAMPLE 6.-S,S-DI-DODECYL CHLOR-OMETHYLPHOSPHONODITHIOATE In a manner similar to Example 1, 40.5 grams of C H SH and 22.0 grams of (C H N were reacted with 16.7 grams of ClCH P(O)Cl to give 49.8 grams of ClCH P(O)(SC H which had an index of refrac tion N =1.4925 and analyzed 6.5% P and 12.5% S. This compares with the theoretical values of P, 6.2%; S, 12.8%.

EXAMPLE 7.S,S-DI-p-CHLOROPHENYL CHLOROMETHYLPHOSPHONODITHIOATE EXAMPLE 8.S,S-DIPHENYL CHLOROMETHYLPHOSPHONODITHIOATE Following the procedure of Example 7, 16.7 grams ClCH POCl and 23.0 grams of C H SH were added to 22.0 grams (C H N at 2530 C. and allowed to reflux. The resulting 0101-1 1 (SC H weighed 26.0 grams and had an index oi refraction N =1.6454.

The class of compounds characterized by the foregoing examples has been found to have valuable plant defoliant properties. Plant defoliants are becoming increasingly valuable :as agricultural aids because of the increased used of mechanical crop pickers. Thus in the case of cotton, it is desirable to have all of the leaves fall off the plant prior to picking in order to produce a cleaner, higher grade of cotton. Such a procedure is also valuable in picking beans and similar crops.

In the followingtest, cotton plants were sprayed with solutions of the defoliant using 1 to 5 lbs./ acre equivalent of'the defoliant in 80 gallons of solution per acre. The procedure used is Well-known in the art. Table I shows the results obtained on cotton plants.

i In conducting the above tests, the percent defoliation in some instances includes leaves which were severely dessicated but had not completely fallen from the plant. The tests definitely show that these compounds provide a new class of defoliants.

The products of this invention may be applied to the plants to be defoliated in the form of solutions, emulsions, dusts or aerosols, according to procedures which are wellknown in the art. In the case of solutions in petroleum solvents or common organic solvents such as alcohols, chlorinated hydrocarbons and so forth, the solution itself may be applied directly or may be dispersed in an aqueous system for purposes of convenience and economy. Dusts may be prepared directly at field strength using the Welllrnown absorbent clays or talcs or they may be prepared as concentrates which may then be diluted with inert diluents for field application. The actual method of preparation and application is not a critical part of this invention but will vary with each compound according to the plant to be defoliated and the conditions under which the defoliant is applied.

The foregoing description is given for clearness of understanding only and no unnecessary limitations should be derived therefrom as modifications will be obvious to those skilled in the art.

We claim:

1. A method of defoliating plants which comprises. ap-

4 plying thereto a defoliating quantity of a compound having the formula u fl 0101121 s R) 3 wherein R is a member of the class consisting of alkyl radicals having up to 12 carbon atoms and monocyelic aryl radicals, X is a member of the class consisting of oxygen and sulfur and n is a number selected from the class consisting of 1 and 0.

2. A method according to claim 1 wherein R is butyl. 3. A method of defoliating plants which comprises applying thereto a defoliating quantity of ClCH P(O) 1-1 4. A method of defoliating plants which comprises applying thereto a defoliating quantity of C1CH2P(O) 3)'3]2 5. A method of defoliating plants which comprises applying thereto a defoliating quantity of ClCH P( O) (SCH CH CH CH 2 6. A method of defoliating plants which comprises applying thereto a defoliating quantity of ClCH P (S) (SCH CH CH CH 2 7. A method of defoliating plants which comprises applying thereto a defoliating quantity of ClCH P (SCH CH CH CH 2 8. A method of defoliating plants which comprises applying thereto a defoliating quantity of 2 (SC12H25)2 9. A method of defoliating plants which comprises applying thereto a defoliating quantity of 10. A method of defoliating plants which comprises applying thereto a defoliating quantity of CICH P (0) (SC H Cl 2 References Cited in the file of this patent OTHER REFERENCES Shepeleva et al., Proc. Acad. Sci. USSR, Sect. Chem. (English translation) 106, 457458 (1956). 

1. A METHOD OF DEFOLIATING PLANTS WHICH COMPRISES APLYING THERETO DEFOLIATING QUANTITY OF A COMPOUND HAVING THE FORMULA 